Downlink inter-cell, or co-channel, interference is a major limiting factor on downlink performance in cellular communications networks, such as 3rd Generation Partnership Project (3GPP) Long Term Evolution (LTE) networks. Various schemes have been proposed and implemented to address downlink inter-cell interference at the network side (e.g., coordinated scheduling). However, even when using these network side inter-cell interference mitigation schemes, there is a substantial amount of residual downlink inter-cell interference. As such, interference aware receivers have been proposed for User Equipment devices (UE), or terminal, side interference mitigation. These interference aware receivers provide improved performance as compared to conventional receivers that treat downlink inter-cell interference as All White Gaussian Noise (AWGN).
Recently, 3GPP created a new study item for LTE Release 12 on Network Assisted Interference Cancellation and Suppression (NAICS) (see “Network-Assisted Interference Cancellation and Suppression for LTE (Release 12),” 3GPP Technical Report (TR) 36.866 V1.1.0, November 2013.). UEs using NAICS (which are sometimes referred to herein as NAICS UEs or UEs having NAICS receivers) have advanced, often nonlinear, receivers that cancel and/or suppress transmissions from interfering cells. Such UEs may need to determine interference parameters in order to use their advanced reception capabilities. The parameters are determined through assistance signaling and/or by making estimates of (i.e., ‘blindly detecting’) the interference parameters. The complexity of blind detection generally increases, and the reliability of blind detection degrades, with the number of parameters and the number of possible values of the parameters. Therefore, more complex downlink transmissions such as those using a larger number of Common Reference Signal (CRS) ports can potentially have higher complexity and lower blind detection reliability.
More specifically, NAICS UEs receiving CRS based transmission modes may need to blindly detect at least the rank and precoding matrix used on one or more interfering Physical Downlink Shared Channels (PDSCHs) transmitted from other cells. If the interference is transmitted using two CRS ports, a total of six precoding matrices could be used, namely, four precoding matrices for rank 1 transmission and two precoding matrices for rank 2. However, if the interference is transmitted using four CRS ports, a total of 64 precoding matrices could be used, namely, 16 precoding matrices for each of ranks 1 through 4). Because of this much larger number of precoding matrices in the four CRS port case, the blind detection complexity and/or reliability can be more challenging than for two CRS ports.
NAICS receivers represent an evolution of prior interference cancellation and suppression receivers. The most straightforward class of interference to cancel is that which has a known pattern or slowly varying information content. CRS interference cancellation, standardized in 3GPP LTE Release 11, is an example feature that cancels interference with a known pattern (in this case interference from a physical signal). Common control channel interference cancellation, also specified in 3GPP LTE Release 11, is an example of cancelling interference from a physical channel with slowly varying interference content. NAICS then is a further enhancement that supports interference suppression and/or cancellation of a physical channel with potentially rapidly varying information content (e.g., the PDSCH).
As discussed above, NAICS receivers require blind detection of a number of interference parameters. In the case of a physical channel with potentially rapidly varying information content (e.g., PDSCH in LTE), this blind detection is complex and may suffer from lower than desired reliability, particularly under certain scenarios. As such, there is a need for systems and methods that lower the complexity and increase the reliability of blind detection in a NAICS receiver.